Known boiler systems typically employ an outdoor sensor to assess the difference between the outdoor ambient air temperature and the temperature of the air inside a structure to be heated. The outdoor sensor responds to the outdoor air temperature to adjust the set point temperature of the boiler. The set point temperature is decreased in warmer weather and in colder weather the set point is increased. This technique is referred to as “outdoor reset.”
There are, however, limitations to using outdoor reset systems. For example, the outdoor sensor requires a puncture through the wall. The outdoor sensor must also be positioned such that it reflects the average temperature of the outside air around the structure to be heated. Significantly, the sensor must not be influenced by the sun's radiation, snow, ice, or other heat sources. Sensors must also be calibrated periodically to ensure proper performance. Additionally, the “reset ratio”, i.e., the change in boiler set point for a change in outdoor temperature must be programmed into the boiler control. Since there is no “feedback”, the reset ratio is typically set very conservatively to ensure sufficient heat is available to maintain home comfort and the effectiveness of the outdoor control to reduce energy consumption is severely limited.
Furthermore, sources of heat gain or loss not related to outdoor air temperature, e.g., open windows and heat generated by human occupation, are not captured by the sensor. Constraining the set point of a boiler may compromise comfort in systems where a minimum boiler water temperature is necessary to ensure comfort. Finally, outdoor reset systems cannot be used with fixed set point boilers.
In view of the above, outdoor reset sensors often obtain erroneous measurements of outdoor air temperature. If the outdoor air measurement is erroneous, the set point established for the boiler can result is insufficient heat to satisfy the thermostat(s).
With the foregoing problems and concerns in mind, it is the general object of the present invention to provide a modulating boiler system in which the energy input to a boiler is reduced, and efficiency thereby increased, without the limitations of an outdoor reset system or the use of an outdoor air sensor.